Effect of zero-valent iron and iron-carbon particles on the denitrification efficiency of anammox process under gradual cooling conditions

Abstract

Nitrogen pollution in water bodies mainly comes from industrial wastewater discharge, urban sewage discharge, and agricultural pollution. Nitrogen in a nitrate form can adversely affect human health and the environment. In this study, the effects of adding zero-valent iron (ZVI) and iron-carbon (Fe-C) particles on the performance of the anaerobic ammonia oxidation (anammox) process and sludge properties under gradual cooling conditions were investigated. Inoculating a portion of mature anammox granular sludge can speed up the rapid start of anammox. After 90 d of domestication and cultivation, the sludge granulation was achieved, and the influent load was increased. After 30 d of incubation, the total nitrogen (TN) removal efficiency can reach 95.08%. Through batch tests, the short-term effects of adding ZVI and Fe-C particles on anammox sludge were studied. It was found that when 100 mg/L dosage of ZVI was added, the denitrification effect of anammox sludge is the best. When Fe-C particles with Fe/C ratio of 2:1 were added, the anammox sludge had the best denitrification effect. Fe-C particles addition increased the pH of the reaction environment and sludge activity was affected. Continuous flow experiments under gradual cooling conditions showed that the effect of adding Fe-C particles on anammox was better than that of ZVI. After adding ZVI under 15 °C, NH 4 + -N and NO 2 - -N removal efficiency was 78% and 86%. Compared with the low temperature non-dosing ZVI, TN removal load was 1.77 kg/(m 3 ·d), and efficiency was improved by 10.2%. Addition of Fe-C particles promoted the denitrification efficiency, NH 4 + -N and NO 2 - -N removal efficiency was 83.90% and 88.84%. As compared to control the TN removal load was 1.90 kg/(m 3 ·d), and efficiency was improved by 8.4%. The sludge concentration showed a positive correlation with temperature. Results from this study show that simple addition of ZVI and Fe-C particles can stimulate microorganisms to secrete more EPS even under lower temperature. The outcomes of study are significant for wastewater management and pollution control in the waterbodies.